The present invention is a process for manufacturing methyl chloride. The process consists essentially of contacting hydrogen chloride with at least a stoichiometric amount of methanol split into at least two portions with a first portion comprising about 60 to 95 percent of the methanol added to the process in the presence of a first liquid medium at a temperature in the range of about 115.degree. C. to 170.degree. C. to form a gaseous mixture containing methyl chloride, and contacting the gaseous mixture with a second methanol portion and adding to a second liquid medium at a temperature in the range of about 100.degree. C. to 160.degree. C., and separating and recovering the methyl chloride.
The preparation of methyl chloride by contacting hydrogen chloride with methanol has been conducted using catalyzed processes in gas and liquid phases. Moreover, many processes are carried out using an excess of hydrogen chloride relative to methanol resulting in unreacted hydrogen chloride and dimethyl ether as a by-product. Due to the corrosive nature of hydrogen chloride and the ecological concerns of discharging hydrogen chloride into the environment, unreacted hydrogen chloride recovery is a time and capital intensive process. Furthermore, it is difficult to recover unreacted hydrogen chloride because it forms an azeotropic mixture with water which makes separation by distillation extremely difficult. In a typical process for removing dimethyl ether from methyl chloride, the methyl chloride is contacted with concentrated sulfuric acid producing a dilute sulfuric acid stream contaminated with methyl sulfates. Formation of the dilute sulfuric acid stream is wasteful in terms of greater raw material costs, and disposal of unwanted sulfuric acid containing dimethyl ether presents ecological concerns as well.
Bunce et al., U.S. Pat. No. 4,935,564, describe a process for preparing an alkyl halide from contacting and reacting a hydrogen halide with a stoichiometric excess of alcohol in a plug-flow reactor in which flow of a mixture comprising unreacted alcohol, unreacted hydrogen halide, the alkyl halide, and water is co-current.
Petrosky, U.S. Pat. No. 4,922,043, describes a process for making methyl chloride by catalytic hydrochlorination of methanol in the liquid phase by feeding hydrogen chloride into a first reactor while splitting methanol feed between or among the reactors. The process uses a stoichiometric excess of hydrogen chloride to methanol and requires a hydrogen chloride recovery system.
The present inventors have discovered that by feeding all the hydrogen chloride into a first reactor and splitting the methanol feed between multiple reactors, reduced levels of dimethyl ether by-product were demonstrated by proportionately increasing methanol fed to a second reactor and proportionately decreasing methanol to the first reactor. Furthermore, feeding a stoichiometric excess of methanol relative to hydrogen chloride results in a higher hydrogen chloride percentage conversion to methyl chloride. Increasing the hydrogen chloride conversion percentage to methyl chloride eliminates processing steps for hydrogen chloride recovery and recycle. Decreasing dimethyl ether formation reduces sulfuric acid use and the ecological concerns and disposal cost associated with sulfuric acid use.